The present invention relates to an apparatus and method for the production of synthetic fibers. In particular, the invention relates to an apparatus and method for the production of spun synthetic fibers having improved uniformity and production efficiencies.
The expanding use of synthetic fibers has had a significant impact on the textile industry. Synthetic fibers are now used in many textile applications where natural fibers were traditionally used. This movement to the use of synthetic fibers mainly has been facilitated by their typically superior physical properties and relatively low manufacturing costs. In addition, synthetic fibers can be tailor-made to have a variety of different properties in order to enhance their applicability in numerous types of applications such as clothing, roping, industrial materials, and many other applications. For example, the material used, the fiber cross-sectional shape, the fiber size, etc. can be pre-selected to form a fiber which has the requisite features preferred for its intended end use. Further, where varieties of features or properties are required, multi-component synthetic fibers can be produced and utilized, with the individual fiber components being selected to provide specific features. In the production of such multi-component fibers, the manufacturer can control the cross-sectional shape of each of the various components as well as their relative proportions in the fiber structure. In this way, multi-component fibers enable a user to capitalize on the particular features of multiple different synthetic materials simultaneously, often with synergistic results.
The most common methods for producing synthetic filaments are spinning processes. Relatedly, such spinning processes also form intermediate stages in the production of nonwoven fabrics such as during spunbonding and meltblowing nonwoven fabric production processes. In these spinning processes, a flowable material (e.g., a solution-dissolved or molten polymer) is fed in a selected manner to a spinneret. The liquified material passes through the spinneret where it emerges in a plurality of thin material streams which are quenched (e.g., by a gaseous or liquid medium) in order to solidify the flowable material streams, thereby forming spun filaments.
Typically, when a plurality of synthetic fibers are produced, it is desirable for the individual fibers of the plurality to have relatively uniform cross-sectional dimensions, in order that uniform properties are consistently provided by each fiber. In commercial manufacturing environments, however, irregularities in fiber structures are commonly and undesirably introduced during fiber production, and variations can occur between the individual fibers relative to each other as well as along the length of each individual fiber.
One example of synthetic fiber production is described in U.S. Pat. Nos. 5,162,074 and 5,344,297 to Hills. In the manufacturing processes described in those patents, flowable polymer material is passed under pressure to etched distribution plates containing horizontal flow paths. The polymer material flows from an inlet point through these flow paths on the etched plate, where it is directed into the backholes of a spinneret. These horizontal flow paths can present several problems in the manufacturing process.
First, because the etched plate is designed to receive the flowable polymer material and to distribute it to the spaced backholes of the spinneret, the individual flow paths of the etched plate would thus, absent any intentional modification to their design, generally have different lengths and/or dimensions. This difference in the path lengths can cause the flowable polymer material in the longer flow paths to experience a larger drop in pressure than the polymer material in the shorter flow paths. This pressure differential between the materials in the different flow paths can thus cause the feed rate of the flowable polymer material to the spinneret backholes to vary, which can adversely affect the shape of the polymer streams exiting the spinneret. These pressure differentials can represent an even greater problem in the production of multi-component fibers, since the feeding of the flowable materials to form particular multi-component fibers typically needs to be very precise.
Because in the prior art methods the pressure irregularities are introduced downstream of the pressure regulating means (i.e., generally a metering plate proximate the material supply point), the pressure irregularities tend to manifest themselves directly in the form of irregularities in the spun fibers. To combat this problem, prior art methods have employed distribution plates where the shorter path lengths are intentionally lengthened so as to equalize the lengths for all of the flow paths. In other words, some channels are made longer than necessary, to achieve a particular fiber construction. This lengthening of the channel increases the dwell time of the flowable material, which can lead to undesirable and otherwise unnecessary polymer degradation. In addition, the extended length channels consume plate area which might be otherwise beneficially used. As a result of this loss of space, cross-sectional design complexity of the fibers can be limited, since more complex designs typically require more channels (and thus more plate space). In addition, the hole density in the spinneret must be correspondingly reduced, since the holes must be located farther apart when the channels take up a greater proportion of plate space. As a result, the through-put rate (and thus productivity) can be undesirably reduced.
Another problem can be experienced when the flow paths of a distribution plate are connected to exit holes with large cross-sectional dimensions. As the polymer material flows from the flow path into the distribution plate exit hole, more of the polymer material is distributed to the area of the exit hole nearest to the flow path outlet than to the opposite sides of the exit hole. This causes an uneven distribution of flowable polymer material to be fed to the spinneret, and as a result, generally precludes the use of the shape and size of the exit hole of the distribution plate in helping to determine the cross-sectional distribution of the respective polymers in the resulting fiber. Consequently, distribution plate designers generally must avoid the use of large and shaped exit holes. Instead, the cited art allows only the positioning of exit holes relative to each other to determine the multi-component cross-section, which is a less certain method than the one of the instant invention, which allows the use of the size and shape of the exit holes to determine the fiber configuration as well.
Accordingly, there exists a need for a method and apparatus for producing synthetic fibers having improved uniformity and for providing improved control over fiber cross-sectional shape.
In light of the above, it would be advantageous to provide a method and apparatus for improving the uniformity of synthetic fibers, while increasing the ease of achieving complexity of the design of a multi-component fiber cross-section. The present invention provides such consistent uniform fiber spinning by generally restoring and/or initiating a pressure equilibrium to the flowable material streams as they are delivered to the spinneret. This in turn allows the spinneret to produce synthetic fibers with more uniform structures and properties. Because the apparatus in one embodiment of the present invention can be used to actually create the requisite pressure for the spinning process, in that embodiment the pressure equipment located upstream of the distribution plate, such as the pressure and metering plates often utilized to provide pressure in conventional spin pack arrangements, can essentially be eliminated.
These and other advantages are provided according to the present invention by an apparatus for forming synthetic fibers which includes a distribution plate for distributing flowable material in a direction perpendicular to the spinning direction, and one or more metering plates positioned downstream of the distribution plate and likewise oriented perpendicular to the spinning direction. (For purposes of this disclosure, elements described as being xe2x80x9cperpendicularxe2x80x9d are oriented perpendicular relative to the spinning direction, while those described as xe2x80x9cparallelxe2x80x9d are oriented parallel to the spinning direction, e.g., in a vertical spinning operation, elements oriented perpendicularly would be in a horizontal position relative to the vertical spinning direction.)
The distribution plate contains at least one flow path which is in fluid flow connection with at least one generally parallel exit hole which forms a portion of a downstream surface of the distribution plate. It is to be noted that the term xe2x80x9cexit holexe2x80x9d, as used in connection with the instant invention, is meant in its broadest sense to encompass the downstream orifice(s) of a plate or cooperating combination of plates, and is intended to encompass all such downstream cavities regardless of whether larger or smaller than the upstream supply channel opening, and regardless of their shape relative to that of the supply channel. Furthermore, while the term xe2x80x9cdistribution platexe2x80x9d appears in singular form, it is intended to encompass all distribution plate arrangements which perform a flowable material distribution function in the manner described in the instant application. For example, the distribution plate can comprise several plate elements which cooperatively function to direct at least one flowable material to a location other than that in which it would be located when exiting the material supply arrangement located immediately upstream of the distribution plate by either directing it perpendicularly relative to its feed position and/or expanding or shaping the flowable material stream from its input dimensions and configuration. Additionally, it is to be noted that the term xe2x80x9cparallelxe2x80x9d is intended to describe the axis of the exit hole as compared with the general overall flow direction (i.e., upstream towards downstream) of the spinning assembly.
The metering plate contains at least one, and preferably at least two orifices which are desirably positioned immediately downstream of an exit hole of the distribution plate. At least a portion of the metering plate orifice (i.e., preferably the downstream portion of the orifice) has a combination of diameter and length sufficient to moderate the pressure of flowable material flowing through the metering plate. In this way, the metering plate achieves a greater degree of equilibration of the pressures of the flowable material(s).
In some instances, the size of the metering plate orifice(s) and the thickness of the metering plate can be specially dimensioned to produce a defined pressure increase in the flowable material. In fact, the metering plate orifice(s) and/or the thickness of the metering plate can be sized to produce a pressure on the flowable material as it exits the metering plate which is alone sufficient for balanced-pressure feed to the spinneret, thereby essentially obviating the need for upstream pressurization means. Furthermore, selected portions of the metering plate can have different orifice configurations, in order to moderate material streams exiting their respective corresponding distribution plate exit holes at different levels.
In the action of the spinneret, it is typically advantageous to have the flowable material oriented in a parallel condition relative to the spinning direction before it enters the spinneret. Thus the metering plate orifice, in a preferred embodiment, orients the flowable material to produce a parallelly-oriented flowable material which is distributed to the spinneret.
In one embodiment of the invention, a second metering plate is also positioned upstream of the distribution plate. In this embodiment, the upstream metering plate provides flowable material to the distribution plate at an initial consistent pressure, with material pressure being re-equilibrated upon exit from the distribution plate by the downstream metering plate.
Typically, a spinneret has a plurality of backholes and mating exit orifices in order that a number of fibers can be spun simultaneously. Therefore, the downstream metering plates used in the present invention desirably have at least one, and preferably two orifices which mate with each of the spinneret backholes which are intended to be active during the spinning process. For some applications, it is advantageous to provide a plurality of flowable material streams to a single spinneret backhole. In light of this, in certain embodiments of the invention, the downstream metering plate has a plurality of orifices which direct flowable material into each of the active individual spinneret backholes. Preferably, at least a portion of each orifice of the plurality is smaller than the distribution plate exit hole to which it corresponds. The plural orifices of the metering plate receive the flowable material from the distribution plate exit hole(s) and output plural flowable material streams. The metering function of the orifices causes the material to flow at equilibrated pressure through each metering orifice fed by the larger, corresponding distribution plate exit hole, rather than flowing preferentially through the metering orifice nearest the channel feeding the distribution plate exit hole. In this way, the plural material streams can be fed to a single spinneret backhole as desired, thereby enabling the pattern of stream feeding to approximate the shape of areas of particular materials in the particular fiber configuration sought to be produced. Such a feeding arrangement has particular advantages in the production of multi-component fibers, as it provides a high degree of precision in the feeding of the stream to the backhole of the spinneret while at the same time, maintaining consistent pressure between the plural streams.
In many applications using this multi-stream embodiment, it is advantageous to have equilibrium between each individual stream of the plurality of flowable material streams. Therefore, in this embodiment, the size of the individual orifices of the plurality of metering plate orifices and the thickness of the metering plate are desirably sufficiently uniform such that the pressure of any one of the plurality of streams is approximately equilibrated to the pressure of any other stream of the plurality of flowable material streams as they exit the metering plate and flow toward the spinneret.
Some synthetic fiber forming applications require the flowable material to be distributed to different areas of the spinneret. In this embodiment, the distribution plate may contain at least two flow paths which each distribute the flowable material(s) to at least one distribution plate exit hole located at a desired position on the distribution plate. Due to this configuration, the flow paths may be of differing lengths and thus provide different pressure losses to the flowable polymer streams. This problem, left unmodified, would result in flowable polymer streams with differing pressures. To counteract this, in one embodiment of the invention, the shape, configuration and dimensions of orifices in the metering plate and the thickness of the metering plate are such that the pressure increase through any exit hole of the plurality of exit holes in the metering plate is large enough to thereby produce a plurality of flowable material streams where the pressure of one stream of the plurality of flowable material streams is approximately equilibrated to the pressure of any other stream of the plurality. In a particularly preferred form of this embodiment, each flow path in the distribution plate includes at least one exit hole such that the individual streams are combined downstream of the distribution plate. For example, the material streams may be combined in shaped cavities immediately upstream of the metering plate, although in most cases they will be combined in the spinneret backhole just downstream of the metering plate. This embodiment of the invention has particular applicability to the production of multi-component fibers, as it enables precise positioning of each of the fiber components.
In some synthetic fiber constructions, it is advantageous to produce synthetic fibers where the fiber contains many shaped aspects, such as a shaped core and shaped outer sheath. In this instance, the distribution plate exit hole(s) can be formed in predetermined shape(s) for producing and distributing a flowable material stream with a predetermined shape. In this embodiment, the metering plate is desirably configured such that a plurality of metering plate orifices correspond to at least one of the distribution plate exit holes. The plurality of orifices of the metering plate which receive each of the shaped flowable material streams then output to the spinneret a plurality of flowable material streams which collectively substantially maintain the predetermined shape. In a particularly preferred embodiment, the plurality of orifices in the metering plate outputs to a spinneret backhole a plurality of flowable material streams, wherein the pressure of one flowable material stream is approximately equilibrated to the pressure of any of the other flowable material streams.
In addition, the invention involves a process for increasing the consistency of synthetic fibers produced in a spinneret. The process involves directing a flow of material across a distribution plate and thereafter through a hole to an adjacent metering plate which moderates and more consistently controls the pressure of the flowable material. Generally this is performed by providing a metering plate which has a downstream orifice that is smaller than the exit hole of the distribution plate, although other forms of metering plate could be used, such as a metering plate having metering orifices which are larger than the distribution plate exit hole, but with the metering holes being long enough for drag from the hole walls to produce the desired pressure drop. After this moderation, the equilibrated pressure flowable material streams are directed from the exit holes of the metering plate orifices to the backhole(s) of a downstream spinneret.
Thus, in the apparatus and process of the present invention, the metering plate downstream of the distribution plate can serve to improve the balance of pressures between a plurality of flowable material streams (whether they are being fed to a single or to plural spinneret backholes) and to create pressure in the flowable material streams, in some cases to an extent sufficient to obviate the need for upstream pressure means.
In another embodiment of the invention,the distribution plate exit hole dispenses a flowable material having a predetermined cross-sectional shape to a plurality of orifices in the metering plate. The higher resistance met by the polymer trying to flow through the metering orifices causes it to fill the upstream shaped cavity before it is able to flow steadily through the metering orifices. Thus, in this embodiment, the plurality of orifices in the metering plate desirably adjust the pressure of the shaped flowable material and produce a plurality of flowable material streams which collectively maintain the predetermined shape such that the flowable material is fed to the downstream spinneret backholes at relatively balanced pressures in a shape which approximates that desired for a particular portion of the cross-section of the spun fiber. As a result, more precisely defined and uniform fiber cross-sections can be produced along the entire fiber length.
Further, the apparatus of the present invention also promotes efficiency in the forming of synthetic fibers. The orifices of the metering plate can be designed with appropriate dimensions such as to create the requisite pressure for the spinning process. This in turn would alleviate the need for the conventional metering plates which are placed upstream of the distribution plate, which is particularly desirable due to the high costs typically associated with these plates. Because the feeding of the flowable material can be more consistent in the apparatus and process of the present invention, better uniformity in fiber-to-fiber cross-sections and better control over the cross-section of each individual fiber can be achieved.